“Thin-walled” nozzle tips are desired for use in injection molding applications due to their small size, which allows the use of multiple nozzle tips within a single mold, for example, in high cavitation applications. In order to provide the material properties required for these applications, thin-walled nozzle tips are typically formed from concentric portions composed of different materials. The inner portion, which contains the channel through which molten material is delivered to the mold, must be made from a highly thermal conductive material. Such materials generally have relatively poor strength characteristics. To protect the low strength inner portion, the outer portion is preferably manufactured from a significantly higher strength material. An example of a concentrically formed, thin-walled nozzle tip is described in U.S. Pat. No. 6,164,954.
A significant drawback of these designs is the fact that highly conductive, low strength inner portion forms the sealing face between the nozzle tip and the nozzle housing in which the tip is mounted. In particular, as shown in U.S. Pat. No. 6,164,954, these designs incorporated an inner portion having a flange that extends above the outer portion. This flange seats directly against the nozzle housing. This arrangement leads to the inner portion being directly exposed to extremely high melt pressures, exceeding 40,000 psi, and load transmissions from torque applied to the threaded joints of the nozzle tip. Because the inner portion is made from a relatively low strength material, it frequently fails under these conditions in the form of seal failure and cracks that ultimately result in plastic leakage.
It would be desirable to provide an improved thin-walled injection nozzle tip capable of withstanding high melt and torque pressures without failure of the highly conductive, low strength inner portion of the nozzle tip.
It would also be desirable to provide the sealing function to the nozzle housing with the higher strength outer portion and by doing so, there is one less interface to seal, since the inner portion flange of the prior art is eliminated from the sealing assembly.
The present invention is directed to meeting one or more of the above-stated desirable objectives.